1. Field of the Invention
The present invention relates to T lymphocytes having an activity of inducing T lymphocytes which recognize an antigen, a method of inducing specific antigen-specific T lymphocytes, use of induced T lymphocytes as a therapeutic agent for cancer or an infectious disease, HLA-A2402-restricted cytotoxic T lymphocytes (CTLs) specific for a tumor-associated antigen, an antigen peptide recognized by the CTL, use of the antigen peptide as a CTL inducer and a therapeutic agent for cancer, and a tetramer formed by tetramerizing MHC/antigen peptide complexes which is useful for detection of the CTL.
2. Discussion of Related Art
Among cytotoxic T lymphocytes (CTLs), there is a CTL capable of recognizing, by a specific T cell receptor (abbreviated hereinafter as “TCR”), a complex wherein an antigen peptide and a major histo-compatibility antigen MHC molecule encoded by a major histo-compatibility gene complex (abbreviated hereinafter as “MHC”) are bound to each other, thus injuring cells presenting the complex on the cell surface thereof. The major histo-compatibility antigen MHC molecule, in the case of humans, is called human leukocyte antigen (abbreviated hereinafter as “HLA”). The CTL recognizes and injures only a target cell having the same HLA molecule as in the CTL itself. Accordingly, the CTL is called “HLA-restricted CTL”.
The cytotoxicity reaction can be generated by:    1) the presence of a CTL having a specific TCR, and    2) the presence of an antigen peptide not only capable of binding to an HLA molecule but also forming a complex recognized by the TCR in order to become an antigen peptide presented by an HLA and recognized by the CTL.
Such antigen peptide is generated, for example, by processing, in an endoplasmic reticulum, of an antigen and the like such as a protein synthesized intracellularly in a mammalian cell, to degrade the antigen and the like into smaller epitope peptides. The antigen peptide is further associated with an HLA molecule and presented on the surface of a cell. I.e., the protein is degraded into peptides consisting of from 8 to 15 amino acid residues in a proteosome complex consisting of many subunits, and some of the generated peptides are transported from the cytosol to an endoplasmic reticulum by a TAP transporter. The peptides, when bound to a class I/β2 microglobulin heterodimer in the endoplasmic reticulum, are stabilized as a 3-molecule complex and transported through a Golgi apparatus into the surface of a cell.
Furthermore, it has been revealed that upon infection with organisms such as viruses, microorganisms, protozoa and fungi, a CTL against an antigen possessed by these organisms plays an important role in protection against infection.
The HLA class I molecules are roughly divided into HLA-A, HLA-B and HLA-C. It is known that an antigen peptide presented upon binding to the HLA class I molecule is composed of from 8 to 10 amino acid residues and has certain structural features which vary depending on the respective HLA molecules. For example, a peptide consisting of from 9 to 10 amino acid residues having a Leu residue at the second position from the N-terminal thereof and a Leu residue or a Val residue at the C-terminal is best known worldwide as a peptide binding to the HLA-A2.1 molecule found most frequently. A peptide consisting of from 9 to 10 amino acid residues having any one of a Tyr residue, a Phe residue, a Met residue and a Trp residue at the second position from the N-terminal thereof and any one of a Leu residue, an Ile residue, a Trp residue and a Phe residue at the C-terminal is best known as a peptide binding to an HLA-A24 molecule abundant in Asians races including Japanese (J. Immunol., 155, p. 4307-4312 (1995)).
Tumor antigens of which antigen peptides have been identified up to now include MAGE-1 and MAGE-3 against HLA-A1; MAGE-3, MART 1, tyrosinase, gp100, HER2/neu, CEA and the like against HLA-A2.1; MAGE-3 against HLA-Cw1; MAGE-3 against HLA-B44; MAGE-A4 against HLA-B37; MAGE-1, MAGE-2, MAGE-3, CEA, HER2/neu, tyrosinase and β-catenin against HLA-A24, and the like.
Many of the antigen peptides have been found by establishing a tumor cell-recognizing class I-restricted CTL, to identify a tumor antigen recognized by the CTL, finding the minimum unit in a protein serving as the tumor antigen by a genetic engineering method and selecting a peptide in the minimum unit, on the basis of information on a binding motif to HLA class I molecule (Proc. Natl. Acad. Sci. USA, 91, p. 3515-3519 (1994)).
The antigen peptide is determined by finding HLA class I molecule-binding peptides consisting of a sequence in a tumor antigen protein, on the basis of a motif structure common in the HLA class I molecule-binding peptide, selecting a CTL-inducible peptide from the found HLA class I molecule-binding peptides, by using antigen-presenting cells, and evaluating whether a CTL having cytotoxicity on tumor cells can be finally induced or not (Proc. Natl. Acad. Sci. USA, 91, p. 2105-2109 (1994); J. Exp. Med., 179, p. 921-930 (1994)).
The HLA class I molecules are classified into some subtypes. The subtype possessed by humans varies significantly among races. The proportion of humans having HLA-A2 is highest in the world and accounts for 45% of the Caucasoid, for example. Identification of the HLA-A2-restricted antigen peptide has advanced most. On the other hand, in the Japanese, the proportion possessing HLA-A2 accounts for 40%. 20% of the Japanese have HLA-A*0201 which is the same subtype as in the Caucasoid, and many of the rest of the Japanese have A*0206. Peptides binding to these subtypes vary depending on the subtype. For example, a mainly studied peptide binding to HLA-A2 is HLA-A*0201. On the other hand, the proportion of the Japanese possessing HLA-A24 accounts for 60% or more. The proportion possessing the HLA-A24 is higher in Asian races than in other races.
The antigen peptide, even if the antigen is the same, varies depending on the type of HLA, and induction of a CTL utilizing the antigen peptide is thus troublesome. To solve this problem, various devices have been made, but satisfactory results have not been obtained yet at present. One of the devices is a method of inducing T lymphocytes by utilizing cells obtained by transducing an antigen gene into antigen-presenting cells derived from a patient himself (autologous). As the antigen-presenting cells, use of B cells, macrophages or dendritic cells, known as professional antigen-presenting cells, have been examined, and a clinical test of using the dendritic cells mainly for vaccine adjuvant and the like is conducted (J. Immunotherapy, 21, p. 41-47 (1998)). In these antigen-presenting cells, however, there are some disadvantages that much labor is required to prepare the cells in a necessary amount to induce immunization. In addition, the B cells have the advantage that the cells can be prepared in a large amount by immortalization with EB virus. Owing to use of the virus, however, there is the disadvantage of lacked generality. With respect to the method of introducing the gene, introduction of the gene using a virus vector or a plasmid DNA has the disadvantage of generating a new variant in some cases by insertion of the gene into a chromosome.